A commonly used type of compressing tool comprises a hydraulic piston-cylinder and a tool head secured to the cylinder head. The article being worked upon, for example, a terminal being crimped, is compressed between movable and fixed dies, the movable die being mounted on the end of a ram which in turn is secured to the piston rod.
Compressing tools of the type described above frequently are highly stressed when used and must therefore be extremely robust and carefully constructed to avoid the possibility of failure of any of the parts, particularly the parts of the hydraulic actuator. It is virtually impossible for a failure to occur in a properly designed and properly maintained compressing tool used in accordance with the manufacturer's recommendation. However, it is always possible that through misuse or lack of maintenance, a failure will occur in the hydraulic system and particularly in the cylinder or cylinder head. The hydraulic pressures in such tools are quite high and return springs are commonly used which are interposed between the cylinder head and the piston to return the piston to its starting position after completion of a crimping or other compressing operation. If a failure should occur at the time in the compressing cycle when the hydraulic pressure is at its maximum level and the spring is compressed to its maximum extent, it is possible that parts of the tool will be propelled outwardly by the compressed return spring since the hydraulic pressure is being maintained during this interval on the piston.
The present invention is directed to the achievement of a fail-safe feature which will prevent any significant movement of any of the parts of the tool in the event of a fracture in the cylinder head or in the cylinder wall. The invention is further directed to the achievement of a fail-safe feature which can be incorporated into the tool without increasing the dimensions of the tool and without in any way interfering with the normal operation of the tool.